Abstract: It is probable to occur many kinds of damage in the area of stress concentration zone when the pressure vessel is in operation, so finding those injury and eliminate the stress concentration is very useful to stable pressure vessel for improving its usage life. This paper is mainly to summarize the basic principle and parameter set of the diagnose equipment of the metal magnetic memory. And it calculated the residual stress distribution of 09MnNiDR butt-welded(WM) and heat affected zone(HAZ) according to the relevant standards with the data being analyzed with one software. The result of the analysis showed that the residual stress of heat affected zone was higher than welding and it was also similar with the result of experimentation and numerical analysis based on the same welding procedure. It revealed that magnetic memory test could find the stress concentration zone of pressure vessels, and could be used for the early diagnosis of pressure vessels.